Milling cutter



Jan. 30, 1923,

F. MULLER. MILLING CUTTERI ORIGINAL FILED SEPT.

11, 1919, 5 SHEETSSHEET 1 51402 'wtoz W MM F. MULLER. MILLING CUTTER. ORIGINAL FILED SEPT. 11. 1919. 5 SHEETS'SHEET 2 awuewbo c Jan. 30, 1923. 1

F. MULLER. MILLING CUTTER. ORIGINAL FILED SEPT 11, 1919. 5 SHEETSSHEET 4 awuewtoz unta/wk I14 4% Jan. 30, 1923.

1,443,641 F. MULLER. MILLING CUTTER. ORIGINAL FILED SEPT. 11, 1919. 5 SHEETSSHEET 5 mm MW Patented Jan. 30, 1923.

UNITED sA Esg PAENT F-Fcs.

FRIEDERICE M'O'LLER, OF HARTFORD, CONNECTICUT, ASSIGNOR TO PRATT & WHIT- NEY COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY.

"MILLING CUTTER. 7

Application filed September 11, 1919, Serial No. 323,110. Renewed March 1922. Serial No. 546,520.

To all whom it may concern: diagrammatic plan and end views respec- Be it known that I, F RIEDERIOH MtiLLER, tively of the milling-cutter shown in Figs.

a citizen of the United States,-residing at 1 and 2. In these 'views there'is shown a Hartford, in the county ot-Hartford and smaller number of teeth and .the inclination 5 State of Connecticut, haveinvented certain of the cutting faces and the reliefqare innew and useful Improvements in Milling creased in order to bring out the principles Cutters, of which the following is a specifiof the invention more clearly. I cation. 'g. 5 is a diagrammatic view illustrat- In the art of cutting metals it is prefer in'g certain'features of the cutter shOWn in 10 able for many classes of work to incline the Figs. 3 and 4.

face of the cutting tool backward with re- Figs. 6 and 7 are side end end views respect to the direction of relative. movement, spectively of a somewhat different formed A thus providing a rake or undercut which cutter embodying the invention; '7 provides asharper cutting edge and enables Fig. 8 is a diagrammatic view showing 15 other advanta es to be attained. Toa limthe eifective contour of the cutter shown in ited extent this principle has been applied F i s. 6 and 7. 1. i to milling cutters, the cutting face being in- 'gs. 9 and. 10 are end and bottom views clined backward with respect to radial lines; respectively of a preliminary milling cutbut it has not heretofore been deemed poster which me be used formilling the final 20 sible to make milling cutters of this type cutter shown-1n Figs. 1 and 2.

which are adapted to accurately cut a pre- Fig. 11 is a diagrammatic view on the determined contour and which are so resame scale as Figs. 3 and 4 illustrating a j li'eved that they can be ground on the cutting slightly difl'erent preliminary cutter diafaces without changing the effective co'ngrammatically and showing itin use for 25 tour. h 1 a milling a blank for a final cutter, the 'mill- In accordance with the present invention, ing operationhav'ing been started butmnot I have provided formed or contour cutters finished. For the sake of simplicity the 1 which are properly relieved and which have blank for the final cutter is shown with their cutting face nonrradial so as to pro radial instead of non-radial cuttingv faces. 30 vide a rake or undercut. The cutting faces Fig. .12 is -a diagrammatic View on the of a cutter embodying the invention may be same scale as Fig. 11 illustrating certain parallel with the axis or they may be infeatures of the preliminary cutter. clined or helicoidal as set forth in my patent Fig. 13 is a view similar to Fig. 11 but for milling cutters, No; 1,348,295,, dated Auillustratingthe blank comple tely milled. 35 gust 3rd; 1920. i Fig. 14 is a view similar .toFigpll but I have shown in the accompanying drawshow1ng the preliminary cutter in operativeingstwo different cutters embodying the inrelation to a' finished final-cutter. vention. and I have illustrated methods by Fig. 15 is a plan view of a lathe tool which they may be made. It will be underadapted to be used for shaping the prelimi- 40 stood, however, that the drawings are for nary milling'cutter.

illustrative purposes only and are not to be Fig. 16 is a diagrammatic view illustratconstrued as defining or limiting the scope ing a method of shaping the preliminary of the invention, the accompanying claims milling cutter, use being made of'the lathe, being relied upon for that purpose. It will tool shown in Fig. 15.

45 be particularly understood that the contours Fig.'.17 is a view similar to Fig. 14 but of the cutters .shown have been selectedjillustrating a final cutter having non-radial merely by way of example and that any or undercut cutting faces and illustrating practical contours may be substituted for the. preliminary cutter shown in Figs. 9 those illustrated. and 10.

50 Of the drawings: Fig. 18 is a view similar to Fig. 16, but

Figs. 1. and 2 are side and end views reillustratinga method of shaping the'prelimspectively of a formed milling cutter eminary cutter shown in Fig. 17. bodying the invention. I Fig. 19 is a diagrammatic view illustrat- Figs. 3 and 4 are enlarged fragmentary ing the method that is followed for cutting the required contour and relief on a cutter blank of the type shown in Figs. 6 and 7 but having radial instead of non-radial cutting faces. A cuttin tool is shown in engagement with the b ank. 7

Fig. 20 is a fragmentary front view of the elements shown in Fig. 19.

Fig.21 is a diagrammatic sectional view taken along the lines 2l2l-of Figs. 19 and 20.

' Fig. 22 is a view similar to Fig. 21 but showing the cutter blank and the tool in different relative positions.

Fig. 23 is a diagrammatic view illustrating the supplemental relative movement between the blank and the tool that is required for undercut faces. The three fragmentary tooth sections can .beconsidered as taken 'respectively along the lines 24-24, 25--25 and 26-26 of Figs. 6 and 19.

Figs. 24, 25 and 26 are diagrammatic views similar to Fig. 23 illustrating the blank and the tool relatively adjusted for the respective sections 2424, 2525 and 2626.

Fig. 27 is a diagrammatic plan view of a machine adapted for making the cutter.

Fig. 28 is a sectional view taken along the line 2828 of Fig. 27.

Referring particularly to Figs. 1 to 5 of the drawings, it will be seen that I have shown a cutter C which is shaped to cut a predetermined contour differing from a straight line. The cutter is provided with a plurality of generally longitudinal teeth 1 between which are grooves 2, the teeth and grooves being preferably spaced uniformly. The grooves 2 between the teeth can be of any usual or preferred depth and shape, as required by the spacing and by the depth of the contour to be cut. The front wall 3 of each tooth 1 constitutes the cutting face thereof and this cutting face is non-radial, being inclined backward in order to provide an improved cutting angle. Each cutting face 3 is inclined or positioned obliquely so that its longitudinal lines lie at angles to the axis of the cutter. Preferably, each tooth 1 is generally helical in form and each cutting face 3 conforms to a helicoid. As illustrated, the helicoid is one formed by a generatrix following a helix on a small cylinder concentrio with the axis and also following a. helix on a much larger cylinder also concentric with the axis. faces may be inclined in either direction with respect to the axis and the degree of inclination may be varied as required.

The cutter may be made for cutting any desired practical contour. The contour may be made up of a series of straight lines, or a series of circular arcs, or a combination of circular arcs and straight lines, or the com tour may consist in whole or in art of noncircular curves. The cutter shown is adapted for cutting a contour consisting of The teeth and the cutting Master straight end portions and a convex central portion conforming we circular arc and having a depth 6. It will be understood that this particular contour has been selected merely by way of example and that the contour can vary in any practical way that may be desired, the method being particularly applicable however for making a cutter having a curved contour.

The outer edge of each cutting face 3 has an outline which is adapted to cut the pre determined contour when the cutter is rotated, this outline of the cutting face following the helicoidal surface thereof. This will be more-clearly understood from the diagrammatic views in Figs. 3 and 4. For the particular contour illustrated, the four points 4, 5, 7 and 8 on the outline of the cut ting face are all at equal distances from the axis of the cutter; the central point 6 is at a distance from the axis which is less by the distance Z); and all other points along the put-line are at their respective correct distances from the center so that when the cutter is rotated they will define the correct predetermined contour, as shown by full lines in Fig. 5. This relationship of the several points along the out-line of the cutting face obtains notwithstanding the fact that the cutting face is a non-radial warped or helicoidal surface.

Each tooth of the cutter is relieved along lines 9 extending backward and inward from the outline of the non-radial cutting face, these relief lines forming a continuous surface or continuous surfaces which extend from end to end of the cutter. The relief lines are properly constructec notwithstanding the variations in radius at different points along the said outline and notwith standing the variations in angular position resulting from the non-radial warped or helic-oidal cutting face. Preferably the relief lines 9 are maintained in similar relationship to each other as they extend backward and inward. the lines conforming to spirals or Archimedes. The result is that each tooth of the cutter. at any axial plane of intersection, such as 55, has a distorted shape, as shown by dotted lines in Fig. 5. This distorted shape includes points 1 1, 15. 16, 17 and 18 corresponding respectively to the points 4, 5, 6, 7 and 8 on the outline of the cutting face. The distortion of shape results from the fact that the successive inward inclined relief lines 9 start at different angular positions because of the non-radial helicoidal cutting face. therefore with the cutting face inclined in the direction illustrated the several points 17, 16, 15 and 14 to the left of the point 8 or 18 are spaced inward from the respective points .7 6, 5 and 4 by progressively increasing distances. Notwithstanding this distortion in shape at an axial plane of intersection, the outline or effective contour at the cutting face is correct, as before stated.

WVhen the relief lines 9 conform to spirals and are maintained in similar relationship as they extend backward and inward, as is preferred, it is possible to sharpen or grind the teeth of the cutter on the front cutting faces 3 without changing the effective contour. The teeth present the same effective contour at successive non-radial helicoidal surfaces of intersection similar in form and position to the initial cutting faces 3. At

any surface, such as e-e, back of an initial cutting face 3 and similar to the said face,

the same effective contour will be found.

straight line. The cutter is provided with.

a plurality of generally longitudinal teeth 19 between which are grooves 20, the teeth and grooves being preferably spaced uniformly. The grooves 20 between the teeth can be of any usual or preferred depth and shape, as required by the spacing and by the depth of the contour to be cut. .The front wall 21 of each tooth 19 constitutes the cutting face thereof and. this cutting face is non-radial, being inclined backward in order to provide an improved cutting angle. The cutting faces may be plane or parallel with the axis of the cutter, but it is preferable to incline them so that the longitudinal lines of each face lie at angles to the axis. Preferably, as shown, the entire teeth 19 are oblique or inclined, and not merely the front cutting faces 21 thereof, and each tooth 19 is .generallylielical in form and each cutting face-21 conforms to a helicoid. As illustrated in Figs. 6 and 7, the helicoid is one formed by a generatrix following a helix on a small cylinder concentric with the axis of the cutter and also following a helix on a much larger cylinder also concentric with the axis. The teeth and the cutting faces may be inclined in either direction with respect to the axis and the degree of inclination may be varied as required.

The cutter D may be made for cutting any desired practical contour. The contour may be made up of a series of straightlines, or a series of circular arcs, or a combination of circular arcs and straight lines, or the contour may consist in whole or in part of non-circular curves. The cutter shown in Figs. 6 and 7 is adapted for cutting the contour shown in Fig. 8, this contour consisting of a straight sect-ion 22 parallel .with the axis, a concave section 23 in the form of a circular arc, a straight section 24 incl ned with respect to the axis, a concave section 25 in the form of a circular arc, a convex section 26 in the form of an elliptical are, a concave section 27 in the form of a circular arc, and a straight section 28 parallel with the axis. The grooves 20 can be of any usual or preferred depth or shape as required by the spacing and by the depth of the contour. groove 20 has a uniform depth throughout;

that is, its bottom is at a uniform distance from the axis of the cutter.

The outer edge of each cutting face 21 has an outline which is shaped to cut the predetermined contour when the cutter is rotated, this outline of the cutting face following the non-radial and preferably helicoidal surface thereof. All points along the outline must be at their respective correct distances from the center so that when As-iilustrated in Fig. 8, each the cutter is rotated they will define the cor- I rect predetermined contour. This relationship of the several points along the outline of the cutting face obtains notwithstanding the fact that the cutting face is non-radial;

and this relationship obtains nothwithstanding the fact that the cutting face is or may be a warped or helicoidalsurface as shown.

Each' tooth of the cutter D is relieved along lines 29 extending, backward and inward from the outline of the cutting face, these relief lines forming a continuous surface or continuous surfaces which extend from end to end of the cutter and which are properly constructed notwithstanding the variations in radius at different points along the said outline and notwithstanding the variationsin angular position resulting from the non-radial and preferably warped or helicoidal cutting face. Preferably the relief lines 29 are maintained in similar relationship to each other as they extend backward and inward, the lines preferably conforming to spirals of Archimedes. The result is that each toothof the cutter, at any axial plane of intersection; has a distorted shape, the distortion of shape resulting in part from thefact that the successive in- I preferred, it is possible to sharpen or grind the teeth of the cutter on the front cutting faces 21 without changing the effective contour. The teeth present the same effective contour at successive inclined surfaces of intersection similar in form and position to the initial cutting faces 21. At any surface,

back of an initial cutting face 21 and similar to the said face, thesame effective contour will be found. Therefore if the cutter is ground on the front faces to helicoids which are the same as the helicoids of the initial cutting faces the efiective contour will remain the same. I

. The two cutters C and B may be distinuished by the fact that in the cutter C the orward outer corner of each tooth is considerably behind the opposite rear outer corner of the next preceding tooth whereas in the cutter D the forward outer corner 7 of each tooth overlaps the opposite rear out-er corner 9 of the next preceding tooth. This difference is an important one, as on account of it, the cutter C can be made by methods that are not adapted for the cutter D. On the other hand the cutter D has important advantages, one of which is that it can be made of any reasonable length. A cutter such as C is limited in length by the width of the grooves 2 between the teeth, whereas a cutter such as D can be much longer as the teeth are permitted to overlap.

To assist in giving a. more complete understanding of my invention, 1 will set forth certain methods by which my improved milling cutters may be made. The present invention is-not limited by the methods which may be used, and it will be understood that methods other than those described may be employed. I will first describe a method which is adapted for the making of the cutter C, @and I will then describe a method which is adapted for making either of the cutters. It will be understood that with either method the preliminary steps of turning the blank, cutting the grooves therein, etc.', can be carried on in any usual or preferred way, these steps not requiring any special description.

The method that I will first describe for making the cutter C is one which is presented and claimed in my copending application for methods of making milling cutters, Serial No. 323,111 filed on even date herewith. The shape of the cutter to be made is formed by means of a preliminary.

milling cutter, this preliminary cutter pref erably acting directly on the final cutter.

Figs. 9 and 10 show a preliminary milling cutter T such as may be used. The cutter T is formed with teeth 30 having grooves 31 between them. As set forth in the said application, each tooth 30 of the preliminary cutter is formed with a helicoidal cutting face 32 having a longitudinal pitch bearing a predetermined ratio to. the longitudinal pitch of the helicoids of the final cutter C; and each tooth is provided with relief lines the opposite direction.

33 having a degree of relief bearing the same predetermined ratio to the degree of relief of the teeth of the final cutter.

Referring tothe diagrammatic Fig. 11, which shows a cutter T very similar to the cutter T, it will be seen that each tooth of the cutter has at any longitudinal plane of intersection such as 1212 a shape which is the same or approximately the same as the predetermined contour to be cut by the final cutter. This is indicated by dotted lines in Fig. 12, the points 4, 5*,6", 7 and 8 corresponding respectively to the points 4, 5, 6, 7 and 8 on the effective contour of the final cutter.

As the result of providing the preliminary T cutter with helicoidal cutting faces and with the relief as shown and described, the contour of each cutting face is distorted, the extent of distortion being-the same in amount as that of the final cutter at an axial plane of intersection as shown by dotted lines in Fig. 5. As shown by full lines in Fig. 12 the distorted contour of the cutter T has points 14:, 15 16, 17 and 18 corresponding respectively to the points, 5, 6, 7 and 8?. The several points 15, 16, 17 and 18 to the left of the point a or 14: are spaced outward from the respective points 5 6 '7 and 8 by progressively increasing distances.

In Figs. 11 and 13 T have shown the cutter T used for shaping a blank to form a cutter C having radial cutting faces. It will be understood that the cutter T" is rapidly rotating in the direction indicated by the arrow thereon i that the blank is bodily toward the axis of the blank, as indicated by the vertical arrow, and then bodily away from the axis of the blank in Preferably the downward or inward relieving movement is so timed that the resulting relief on the blank will conform to spirals of Archimedes, The cutter T is movedslowly downward during the cutting of each .tooth and then is rapidly moved upward'between the teeth to position it for the cutting of the next tooth.

As shown in F ig. 11, the cutter T and the blank have been so adjusted that the teeth of the rotating cutter will mill the initial point at of the tooth of the blank C to the required distance from the axis. The downward movement of the cutter T in timed relation to the slow rotation of theblank causes it to take a out which gradw ally increases in depth at the successive points back of the point 4. As the cutter blank C is slowly turned and as the out ter 1" is fed downward in accordance with the relief, the parts move to the position shown in Fig. 13, the distorted shape of the cutter T exactly compensating for the distortion which would otherwise take place in the shape of the cutter C. The cutter T shapes the cutter C with the several points 4, 5, 6, 7 and 8 all at the proper distances from theaxis, so that the cutter C when used will generate the true contour, as shown by full lines in Fig. Referring to Fig. 14, it will be noted that the dot-and-dash line liqh represents in a general way the direction of relative movement of the preliminary milling cutter in forming the relieved outline of the'tooth on the cutter C. As the preliminary cutter T is rapidly rotating its plane of maximum depth of cutting will necessarily be perpendicular to the line lc-k. Cutting to the maximum depth of contour will therefore be effected at a plane such as ZZ perpendicular to the line 7c7. The transverse shape of the tooth of the cutter C will therefore be determined as the successive parts of the teeth pass the plane ZZ. But.

when the cutter C is afterward used'in'a milling operation it will cut to its maximum depth and determine the contour of the body being cut ata plane such as mm passing through the axis. Clearly the planes ZZ and mm are not and cannot be parallel, there being an angle such as n included between them. The depth distance Z) of the final cutter measured along the plane m-m is slightly greater than the depth distance I) of the preliminary cutter measured along the plane Z-Z, the amount of the difference being dependent on the angle of relief. Therefore, if the preliminary cutter has exactly the predetermined shape at axial longitudinal planes of intersection,

a slight error in the shape of the final cutter results from the fact that the shape is formed at the plane Z-Z and used at the plane 122-712. This error is very slight and for many classes of work can be treated as entirely negligible. However, for work requiring the very highest degree of accuracy it may be desirable to correct this error.

Fig. 15 shows a lathe tool V-having a contour 4", 5", 6", 7 i which is exactly the same as the predetermined contour 4. 5, (3, 7, 8, which'is to be finally cut by the cutter. This tool is used in a relieving lathe to shape the preliminary cutter T as illus trated in Fig. 16. The tool V is set with its cutting face in a. non-axial plane, an angle such as 0 being included between the cutting face of the tool and 'a plane such as 72- through the axis of the cutter. When the preliminary cutter is being depth 1) at the plane Z-l must be slightly decreased. Therefore the contour of the preliminary cutter is slightly changed by decreasing the radial dimensions to an ex tent dependent on the angle of relief of the final cutter. In Fig. 16 the plane pp corresponds in a general wa to the plane -Z--Z, and by setting the too at an angle,as

indicated, the depth 6 of the contour at the plane ;pp is made slightly less than the full depth 6 measured along the top plane of the tool V. From the foregoing description it will be seen that, by the method illustrated, the depth of the contour of the final cutter C at the plane m-m is properly corrected.

The cutter C with non-radial or under-. cut cutting faces is fragmentarily illustrated in Fig. 17 in conjunction with the preliminary cutter T. It will be seen that the front faces of the teeth are so formed that planes perpendicular to the axis of the cutter will intersect, not along radial lines, but along lines such as gg each at an angle such as q to the corresponding radius. If it be assumed that the external helix of generation is the same for the cutter as for the cutter C the outermost points 4, 5, 7, and 8 will not be changed from the positions occupied by the corres onding points 4, 5, 7 and 8 of the cutter 6 as shown in Fig. 14. All other points, however, such as the point 6, spaced inward from the periphery willzbe located further back along the. relief lines and would "therefore be nearer the axis of the cutter if the cutter were to be milled by a cutter T", in the wa shown in Figs. 11 and 13. Tea-void this error the depth I), measured along the plane Z'Z' perpendicularly to the relief, is decreased to an extent dependent upon the non-radial angle of the cutting faces. This decrease is in addition to that already described as necessary to compensate for the angle of relief,

In order that the preliminary cutter T may have the proper depth and other radial dimensions to compensate not only for such as p'p through the axis of the cutter. The angle 0 is somewhat greater than the angle 0 shown in Fig. 16. Inasmuch as the contour has the correct depth b measured along the top face of the tool it will have a slightly shorter depth 6" measured along the plane p-p. When the cutter T is used to mill the cutter C as shown in Fig. 17 it will cut a contour which is of decreased depth b" measured along theplane Z-Z but which has the correct depth 6 when measured radially.

The method which has been described is not in its entirety applicable for making the cutter D, particularly when the cutter is provided with helical teeth. In the described method it is necessary for the teeth of the cutter to be spaced apart so as to enable the preliminary cutter to finish one tooth of the final cutter before engaging the next tooth. When the teeth of the final cutter overlap this is obviously impossible. The cutter D may be made by the method shown in'Figs. 19 to 26, which is presented and claimed in my aforesaid copendin application for methods of making mfiling cutters, Serial No. 323,112 filed on even date herewith. It will be understood that this I method is also applicable for making the cutter C.

In practicing the method, use is made of a cutting tool which is fed alon the blank following the contour thereof. his tool or cutter may be of any usual or preferred type, but l prefer and have illustrated a lathe tool 8. F or roughing out the blank a relatively broad tool may be used, but for funishing it is preferable to usea tool vided with a line point. The tool is held in operative relationship with-a blank and" there is provided a former W having en'- actly the predetermined contour to be cut by the final cutter. The former is engaged by a pin X which has the same or approximately the same front outline as the tool. The former pin is connected with the tool for longitudinal movement in unison therewith.

Figs. 19 and 20 show the tool S in engagement with a blank D which forthe sake of simplicity is shown as having radial instead of non-radial faces, and the pin X is shown in engagement with the former W, the section 22 and a part of the section 23 of the propredetermined contour having already been out. Fig. 21 is a cross sectional View through the blank at the point of engagement of the tool S, the blank being in the position indicated in Figs. 19 and 20. The tool S is shown engaging the front edge of a tooth 1.

In order that the teeth of the cutter may be properly relieved, the tool is reciprocated toward and from the blank axis in timed relation to the blank rotation. As illustrated in. Fig. 21, the blank is rotated in the direction indicated by the arrow and the tool is reciprocated through an effective distance h, the tool being given one complete movement forward and backward for'each tooth of the blank. As shown in Fig. 21, the tool is in its outer operative position and is about to move inward to cut the relief on the tooth which has just come into engagement with it. Fig. 22 is a view similar to Fig. 21 but showing the cutter advanced so that the tool S is at the rear of the tooth .19. It will be clear that the tool has moved inward to its inner operative position and in so moving has formed the proper relief 29 on the tooth.

l have stated that the tool S is reciprocated in timed relation with the rotation of the cutter blank. This relation is definite and fixed if the cutting faces of the teeth are plane and parallel with the cutter axis; but when the cutting faces are inclined or hellcoidal, as shown, the relationship must be varied to conform to thechanging angular position of the outer edge of the cuttin face, as the tool is fed longitudinally. The dotted lines in Figs. 19 and 20 show a different position of the tool S. @n account of the inclination of the tooth the point of the tool is nearthe rear of the tooth instead ofat thepfront thereof, as is shown by full lines. it the same relation had been maintained between the rotation of the cutter blank and the reciprocation of the tool, the tool would he in the sameoutermost operative position which it occupied in Fig. 21, thus leaving. it out of engagement .with the blank. Obviously, the relation between the cutting tool and the blank must be varied in order to enable the tool to cut the necessary relief and at the same time maintain the correct contour. When the front edge of the tooth reaches the point of the tool, the tool must engage the blank and mustthereafter continue in engagement as the tooth continues to move past it. The required variation in the relationship must be such as to maintain the tool and the cutter in the proper relationship as the tool is fed. The

relation between the rotation of the blank and the reciprocating and relievin movements of the tool are continued and t e relative timing is so varied that the tool always engages the front edge of thetooth when the tool is in the outer operative position.

For cutting a blank with non-radial faces, it is necessary to supplementally Vary the ordinary relation between the relieving movements of the tool and the rotative movement of theblank as the cutting tool moves inward or outward to conform to different blank diameters. Therefore, when such a blank is to be cut, the relative movementslheretofore described are somewhat modified. 4

In the diagrammatic Fig. 23 t may. be considered to be a fragmentary sectional view taken at the line 24-.24 of Fig. 6 of a cutter D having undercut faces, the radius of the cutter at this position being 1'. Under the control of the former U and the former pin X, the cutting tool S is at a distance 1* from the blank axis and is in position to engage the point of the tooth shown and cut the properrelief line 29 thereon.

The tooth section taken at the line 2525 of Fig. 1 is shown at t, the radiusat this position being 1". For this radius 1', without special provision being made, the tool S would be in the position indicated by dotted lines at the distance r from the blank axis. However, by reason of the inclined cutting face on the blank, the blank tooth would not be in engagement with the tool but would be separated therefrom by the angle m. The tool, however, would immediately start its inward relieving movement notwithstanding the fact that the blank tooth has not yet reached it, and the result would.

be the cutting of an incorrect relief line 29.

The tooth section taken at the line 26 '-26 of Fig. 1 is shown at t, the radius'at this position being 1'. For this still smaller radius 7", the result would be similar to that last described except that the point of the tooth would "be separated from the tool by a greater angle m, with the result that the incorrect relief line 29" would be further from the correct relief. line 29. In order-to avoid the errors which would occur, as shown in Fig. 23-, I vary the relationship between the relieving movement of the tool and the rotative movement of the blank.

Fig. 24 shows the tool at the position 24-24 and at the distance 'r as shown in Fig. 23. For this maximum radius no variation in position is necessary. Fig. 25 shows the tool at the position 25-25 and at the same radius 11 from the blank axis as was shown in Fig. 23;but the relation of the relieving movement has been so changed that the tooth is in position to be engaged by the point of the tool when the relieving movement starts. The tooth at t is therefore cut with the correct relief line 29. Similarly, Fig. 26 shows the tool at the position 2626 and at the same distance 1'" from the blank axis as was shownin Fig. 23; but the relation of the relieving movement has been so changed that the tooth is in position to be engaged by the point of the tool when the e ective relieving movement starts. The tooth at t" is therefore cut with the correct relief line 29. It will be seen that the operation, as illustrated in Figs. 24 to 26, is in no way efiected byfor dependent on the longitudinal inclination of the-cutting faces In other words, it is immaterial whether the cutting faces be helical or straight.

The required variations in the relationship between the relieving movements of the tool and the rotative movement of the blankcan be brought about either by changing (usually advancing) the blank movement or by changin (usually retarding) thtoolmovements. l have found it simplerto retard thetool movements, and this is particularly desirable when provision is made as herein contemplated for changing the blank movement (and not the relieving movements) to conform to helical teeth. Thereforein practicin the method as illustrated in Figs. 23 to 26, the relieving movements are retarded, the amount of retardation depending on the position of the cutting tool atvarious 'radii less than the maximum radius 1". It will be understood that the retarding of the relieving movements is effected without changing the relative positions of the tool and former pin. The retardation atv the various radii.

is such that thetool is always at-the same position, as concerns its relieving move- ,ments, when it engages atooth of the blank.

most of the details of t e machine, I prefer the construction showni'n my copending 'ap plication for relieving machines, Serial No. 286,524 filed March 31st; 1919.

Referring to Figs. 27 and 28, there is provided a mandrel 30 upon which is carried a cutter blank D, and suitable means are provided for supporting and rotatin the mandrel.. llongitudinally movable a ong ways -cured to the slide 33 is the former pin X,

the shape of which, as before stated, corresponds to that of the tool S, preferably be- 120 31', 31 is a carriage 32 upon which is mountedv I ing exactly the same. Secured to the main frame of the machine is the former W which as already stated, has a contour 22-28 which is exactly the same as the desired effective contour of the finished cutter.

A. spring 36 is provided for pressing the slide 33 toward the rear and thus holding the former pin X always in engagement with the former W. It will be seen that when the carria e 32 is moved longitudinally, the slide 33 Will be caused to move transversely under the, guidance of the former, the tool 8- thus being caused to follow an outline which is exactly the same as that of the former W.

Mounted on the carriage 32 and on the transversely movable slide 33, is a suitable mechanism for reciprocating the slide 34 to effect relieving movements of the tool. Rotatably mounted in a bearing on a bracket 37 carried by the slide is a longitudinal shaft 38 which carries a cam 39. Pivoted to the slide 33 is a lever 40 which at its lower end engages the cam 39 and which at its upper end engages the slide 33. A spring 41 serves to hold the slide 34 in engagement with the lever.

it will be seen that when the shaft38 and the cam 39 are rotated, the lever 40 will be oscillated, thus reciprocating the slide 34 and the tool S. For rotating the shaft 38 and the cam 39, there is provided a longitudinal shaft 42 which is rotated in any suitable way. Splined on the shaft is av worm 43 which is longitudinally movable with the carriage 32. Mounted on the carriage is a transverse horizontal shaft 44 carrying a worm wheel 45 which meshes with the worm 43. Slida-bly mounted on the shaft 44 is a bevel gear 46 which meshes'with a bevel gear 47 on the shaft 38. The bevel gear 46 is engaged by the bracket 37 and is thus held in mesh with the bevel gear 47 as the slide 33 and the parts connected therewith move transversely. The shaft 42 is driven in proper timed relationship with the spindle so that normally, for any givenoposition of the carriage, the cam 39 is given as many complete revolutions for each revolution of the blank as the blank has teeth.

In order that the relieving movements of the tool 8 may be varied in accordance with helicoidal cutting faces on the blank, I preferably provide means for supplementally rotating the blank in proportion to the longitudinal movement of the tool. As illustrated, the mandrel 30 is engaged by a chuck 48 on a spindle 49. Power for rotating the spindle is supplied through a sleeve 50 which has splined engagement with a smaller sleeve 51. A rod 52 and a forked lever 53 are provided for causing the sleeve 51 to move longitudinally with the carriage 32. The spindle 49 is fixed against longitudinal movement and extends into the sleeve 51.

The sleeve 51 is provided with a helical groove 54 having the same longitudinal pitch as the helicoidal cutting faces of-the blank. A pin 55 011 the spindle 49 projects into the groove 54, thus transmitting power from the sleeve 51 to the spindle. It will be seen that the construction permits the spindle to be driven by means of the sleeve 50, but that the spindle is supplementally rotated in proportion to the longitudinal movement of the carriageand the cutting tool. This supplemental movement is just suficient to enable the tool to properly engage the helicoidal teeth.

It has been before pointed out that the bevel gear 46 is slidably mounted on the shaft 44. F or the purpose of changing the relationship between the relieving movements of the tool and the rotative movements of the blank for different diameters, the gear 46 is connected with the shaft 44 by means of pins 56 projecting into cam grooves 57. The inclination and curvature of these cam grooves is such that the relieving movements of the tool are retarded for, .tlle smaller diameters just sufficiently to caiise fthe tool to engage the front edges of the teeth, as clearly illustrated in Fi s. 24, 25 and 26.

What I claim is:

1. A milling cutter having a varying diameter and provided with teeth adapted to cut a predetermined contour, said teeth having non-radial front cutting faces inclined with respect to the cutter axis, the cutting faces of the teeth having a contour different from said predetermined contour but adapted to cut the said contour as the cutter is ro tated, the outer surface of each tooth being relieved behind the non-radial cutting face.

2. A milling cutter having a varying diameter and provided with teeth adapted to cut a predetermined contour, said teeth having non-radial front cutting faces inclined with respect to the cutter axis, the cutting faces of the teeth having a contour different from the said predetermined contour but adapted to cut the said contour as the cutter is rotated, the outer surface of each tooth behind the nonradial inclined cutting face being relieved along lines extending backward and inward from the outer edge of the face.

3. A milling cutter having a varying di ameter and provided with teeth adapted to cut a predetermined contour, each of the teeth having a, non-radial inclined cutting face with a contour differing from the pre determined contour but adapted to cut the said contour as the cutter is rotated, the outer surface of each tooth behind the nonradial inclined cutting faces being relieved along lines extending backward and inward from the outer edge of the face.

4. A milling cutter for cutting a predetermined contour other than a straight line parallel to the cutter axis,'c'omprising a plurality of substantially longitudinal teeth each providedwith a non-radial front cutting face inclined with respect to the cutter axis and having a contour different from the said predetermined contour but adapted to cut the said contour as the cutter is rotated, the outer surface'of each tooth behind the non-radial cutting face being relieved along lines extending. backward and inward from the outer edge of the face to provide an effective contour behind each cutting face which is the same at successive surfaces of intersection similar to the initial cutting face, whereby the cutter may be ground on the non-radial cutting faces without changing the effective contour.

5. A milling cutter for cutting a predetermined contour-rother than a straight line- 6. A milling cutter for cutting a prede-- termined contour other than a straight line, comprising a plurality of generally longitudinal teeth each provided with a non-radial front cutting face inclined with respect to the cutter axis and having a contour difi'er-- ent from the said predetermined contour but adapted to cut the said contour as the cutter is rotated, the outer surface of each tooth behind the non-radial inclined cutting face being relieved along lines extending backward and inward from the outer edge of the face.

7 A milling cutter for cutting a predetermined curved contour, comprising a plurality of generally longitudinal teeth each provided with a non-radial front cutting face inclined with respect to the cutter axis and having a contour different from the said predetermined curved contour but adapted to cut .the said contour as the cutter is rotated, the outer surface of each tooth behind the non-radial in clined cutting face being rebeing relieved along lines extending backward and inward from the outer edge of the face to provide an effective contour behind each cutting face which is the same as successive non-radial inclined surfaces of inters'ection similar to the initial cutting face, whereby the cutter may be ground on the nonradial inclined faces without changing the effective contour,

9. A milling cutter for cutting a predeter-' mined contour other than a straight line,

comprising a plurality of generally longitudinal teeth each provided with a nonradial helicoidal front cutting face having a contour different from the said predetermined contour but adapted to cut the said contour as the cutter is rotated, the outer surface of each tooth behind the non-radial helicoidal cutting face being relieved along lines extending backward and inward from the outer edge of the face.

10. A milling cutter for cutting a predetermined curved contour, comprising a plurality of generally longitudinal teeth each provided with a non-radial helicoidal front cutting face having a contour different from the said predetermined curved contour but adapted to cut the said contour as the cutter is rotated, the outer surface of each tooth behind the non-radial'helicoidal cutting face being relieved along lines extending backward and inward from the outer edge of the face.

11. A milling cutter for cutting a predetermined contour other than a straight line, comprising a plurality of generally longitudinal teeth each provided with a non-radial hellcoidal front cutting face having'a contour different from the said predetermined contour but adapted to cut the said contour as the cutter is rotated, the outer surface of each tooth behind the'non-radial helicoidal cutting face being relieved along lines extending backward and inward from the outer edge of the face and the effective contour behind each cutting face being the same at successive helicoidal surfaces of intersection similar to the initial cutting face,

whereby the cutter maybe ground on the non-radial helicoidal faces without changing the effective contour.

12. A milling cutterfor cutting a predetermined contour other than a straight line, comprising aplurality of generally longitudinal teeth each provlded with a non-radial helicoidal front cutting face having a contour different from the said predetermined contour but adapted to cut the said contour as the cutter is rotated, the outer surface of each tooth behind the non-radial helicoidal cutting face being relieved along linesextending backward and inward from the outer edge of the face and conforming to spirals constructed about the cutter axis.

13. A milling cutter for cutting a predetermined contour other than a straight line, comprising a plurality of generally longitudinal but inclined teeth the forward outer corner of each tooth being in advance of the opposite rear outer corner of the next preceding tooth and each tooth being provided with a non-radial helieoidal front cutting face having a contour differentfrom the said predetermined contour but adapted to 1,4aae41 cut the said contour as the cutter is rotated, 10

In testimony whereof, I hereto aflix my 15 signature.

FRIEDERICH MULLER. 

